I. Field of the Invention
This invention relates to brake bands for automatic transmissions and, in particular, to an improved double wrap brake band and a method of making such brake bands.
II. Description of the Prior Art
Prior known automatic transmissions for automotive vehicles typically utilize a torque converter drivably connected to a series of clutch drums by a shaft. Conventional brake bands wrap around the clutch drums to effect gear changes which in turn varies the speed or direction of rotation of the drive shaft of the transmission. The brake band is hydraulically controlled to shift the transmission from first gear or to reverse the direction of rotation for the reverse gear. Multi-wrap friction bands thereby retard the rotation of the reaction elements in automatic transmissions to affect the necessary gear changes.
Originally, single wrap brake bands were used in automatic transmissions and in some lower torque load applications the single wrap band is still utilized. Essentially, the single wrap band comprises a single band formed in a circle and control brackets mounted to the ends of the band. The brackets were compressed together to compress the single band around the drum. However, such single wrap brake bands proved inadequate in today's high torque/load transmissions.
Early double wrap brake bands were formed from a thick metal strap having lugs engageable by a hydraulic control unit to compress the band around the clutch drum. The ends of the strap overlap such that the lugs of one end of the strap are received by the opposite end of the strap. The prior known methods of manufacturing such early brake bands creates distortion in the band which can cause an undesirable drag on the clutch drum even in the fully open position.
More recent double wrap brake bands employ a preslotted stamped strap to which is attached a bracket member. The bracket is utilized to compress the band and is welded accordingly to the strap. However, the weld set of the bracket is subject to breakage resulting in failure of the band and a limited life for the transmission. Essentially, the increased componentry and complexity of modern brake bands reduces the operational life of the transmission before repairs are necessary. In order to strengthen the connection between the brackets and band, additional brazing was applied to the bracket and band. However, the brazing process substantially increased the manufacturing costs associated with the prior known brake bands.